1. Field of the Invention
This invention relates to strand material covered with a clear flame retardant composition and methods of making same and, more particularly, to telephone cordage jacketed with an extrudable clear flame retardant polyvinyl chloride composition having retractile properties and having protection against degradation by ultraviolet or diffused light while providing stability during manufacture as well as during customer use and methods of making.
2. Description of the Prior Art
Most telephone users are familiar with what is referred to in the art as the spring cord which extends a telephone circuit from a telephone base to a companion telephone handset. It has been the custom to match the color of the line cord, which connects a wall terminal with the telephone base, to the color of the housing of the base, the handset and the retractile cord. Due to the large number of colors and the several different lengths of cords that are available, installers must maintain an uneconomically large inventory of line and spring cords on service vehicles in order to provide the many combinations of length and color. This results in excessive inventory holding costs and requires additional warehouse and truck storage space.
To reduce the excessive costs involved, studies were made to ascertain if a single color cord, which would significantly reduce the number of combinations, could be used. It was decided that this universal color must be neutral in any environment, compliment the telephone set, be aesthetically appealing and be widely accepted by telephone subscribers. Tests showed that a line cord having tinned tinsel conductors individually insulated with a clear nylon material and jacketed with a clear polyvinyl chloride jacket had aesthetic appeal as indicated by a high acceptance rating in product test areas.
Clear flame retardant polyvinyl chloride compositions possessing characteristics required for telephone line cord jackets, have not been commercially available in the past. To obtain flame retardant characteristics, the prior art approach has been to employ additives such as antimony trioxide. This is sufficient if one is working with opaque formulations but the addition of additives such as antimony trioxide to clear polyvinyl chloride compositions is destructive of clarity.
The development of a composition is complicated further by additional demands because of the innumerable environments in which telephones are installed. For example, the final jacketing composition must be flexible and have superior low temperature flexibility properties so that the jacket will not be embrittled in some of the expected environments of use, such as in office buildings prior to placing the heating system in service. Also, the composition must remain clear during the exposure of the cord to ultraviolet radiation in sunlit rooms which tends to degrade the color of plastic covered cords.
In addition, the clear flame retardant jacketing composition must also be of such a nature as to not mar or damage any lacquered surface such as a desk or table top. Also, if the plastic jacket in contact with such a surface does not possess adequate mar resistance, the jacket surface will be permanently damaged.
A clear flame retardant composition for line cords and methods of jacketing line cords therewith is disclosed in copending application Ser. No. 258,964, filed June 2, 1972 in the names of E. S. Sauer and W. C. Vesperman.
While a line cord meeting the requirements set forth hereinbefore is available, the cord connecting the handset to the base presents an added requirement. The composition used to provide a jacket for spring cords must be such that the cord manufactured by jacketing, coiling, heat setting and removal-reversing operations (see U.S. Pat. No. 2,920,348, for example) results in a cord having retractile properties.
When the telephone is not in use, a retractile or spring cord takes the form of a tightly-wound helix. When the handset is removed from the base, the helix expands in a manner of a coil spring to permit the user to range a distance therefrom.
The construction of the spring cord as described in U.S. Pat. No. 3,037,068 issued on May 29, 1962 in the name of H. L. Wessel is designed to permit the repetitive flexure of the cordage for a relatively large number of times as encountered during normal usage. The spring cords must have sufficient retractility to insure that they will return promptly to their normal retracted form after having been extended and released.
Of course, such cords must not be so strongly retractile that they require an excessive amount of force to extend them. If a spring cord is too unyielding, instead of the cord extending when a pull is executed thereon, the instrument to which it is attached may be moved or pulled off its support. Further, it is economically desirable to obtain a desired extended length with as short a length of cordage as possible. Also, from an appearance standpoint, it is desirable that the retracted length of the spring cord be as short as possible.
The helical shape and the springiness of the cord are derived in part from the characteristics of the composition of the jacket surrounding the cord. This adds yet another requirement for the composition of the cord jacket. The composition must endow the cord with retractile properties as well as clarity, and low temperature properties.
Moreover, the composition must be such that the finished cord jacketed with that composition retains its retractile properties. Skin oils, for example, tend to cause plasticizers to migrate from a PVC composition. The composition should be resistant chemically to oils to prevent such migration and thereby preserve the retractility of the cord. This will also avoid the exuding of substances which may be dermatologically adverse to subscribers.